1. Field of the Invention
The present invention relates generally to a system and method for automatic connection and disconnection of a node in a local area network (LAN) to manage power of a LAN controller. More particularly, it relates to such a system and method as implemented with an Ethernet network employing a transmitter/receiver (transceiver) which meets the ANSI/IEEE 802.3 10BASE-T international standard. Most especially, it relates to such a system and method implemented in a media access controller (MAC) for 802.3/Ethernet, also known as MACE, implemented in an integrated circuit including the 10BASE-T transceiver.
2. Description of the Prior Art
Ethernet is a commonly used local area network scheme in which multiple stations are connected to a single shared serial data path. Typically, only one station can transmit data onto the path at a time. A station connected to the path transmits data in the form of a packet that includes a destination address. The packet propagates throughout the network medium and is received by all other stations. The addressed station copies the entire packet as it goes by; the others reject the packet after determining that it is addressed to another station.
A Media Access Controller (MAC) serves as an interface between a shared data path and the stations connected to that path. Each node connected to the network includes a MAC which performs a number of functions involved in the transmission and reception of data packets. For example, during the transmission of data, the MAC assembles the data to be transmitted into a packet with address and error detection fields. Conversely, during the reception of a packet, the MAC disassembles the packet and performs address checking and error detection. In addition, the MAC typically performs encoding/decoding of digital signals transmitted over the shared path and performs preamble generation/removal as well as bit transmission/reception.
Traditional Ethernet is a coaxial wired system. The coaxial cable provides a linear bus to which all nodes are connected. Signalling is accomplished using a current sink technique with the center conductor used for signal, and the shield as a ground reference.
Twisted pair Ethernet in accordance with IEEE Standard 802.3 10BASE-T is able to use standard voice grade telephone cable employing separate transmit and receive pairs (4 wires). The system uses a star topology. At the center of the star is a "repeater". The repeater (or hub) performs signal amplitude and timing restoration. It takes an incoming bit stream and repeats it to all other ports connected to it (but not back to the originating port). In this sense, the repeater acts as "logical coax", so that any node connected to the network will see another's transmission. Differential signalling is employed with one pair acting as the transmit path, and the other as receive. Further details on 10BASE-T Ethernet networks, including a description of the state of the art for such networks, is provided by Crayford, "10BASE-T in the Office," Wescon, San Francisco, Nov. 20, 1991, the disclosure of which is hereby incorporated by reference herein.
Transceivers as used in 10BASE-T Ethernet networks may incorporate a sleep mode, in which a node incorporating the transceiver powers down when there is no activity for it after a predetermined period of time. However, when the node is in the sleep mode, it will miss any transmissions intended for it. It would be desirable to provide the power saving advantages of the sleep mode without resulting in missed transmissions. Efficient network management also requires that nodes on a network be identified as present. With prior art sleep modes, a network controller of a node in sleep mode is treated as if it were disconnected from the network.